I was going to say Xorn, but it wasn't the character that bothered me as much as all of the "it was Magneto, but not really, it was Xorn's brother pretending to be Magneto pretending to be Xorn... I think." It was like he was a dude playing a dude disguised as another dude.

Xorn was a great character. Even better when he was revealed to be Magneto. Then they just pissed all over that.